The present invention relates to a catalyst composition and method of making the same, which composition comprises a carrier having a high surface area refractory metal oxide support coating thereon, on which a catalytic metal is dispersed. More particularly, the present invention relates to an improved catalyst composition and method of making the same in which the carrier is a porous refractory metal oxide material and the catalytic metal comprises one or more platinum group metals dispersed on the coating.
U.S. Pat. No. 3,565,830 discloses catalysts comprising a porous, refractory metal oxide carrier which may be formed as a monolithic skeletal body ("honeycomb carrier") having a plurality of parrallel gas flow passages extending therethrough. The carrier has a high surface area refractory metal oxide support coating on which one or more platinum group metal catalytic components are dispersed. As disclosed in this patent, the carrier may be composed primarily of ceramic-like but porous refractory metal oxides including combined forms, for example, alumina, alumino-silicates, and magnesia-silica-aluminas, e.g., cordierite.
U.S. Pat. No. 4,157,316 discloses a catalyst having both oxidation and reduction catalytic properties and of similar composition to that of the U.S. Pat. No. 3,565,830 patent, but comprising one or more base metal oxides in addition to one or more platinum group metals as the catalytic components.
While suitable refractory metal oxides such as cordierite have desirable characteristics such as high temperature and thermal shock resistance which well suits them for use as honeycomb carriers for catalyst compositions of the invention, their surface area is too low to effectively support thereon dispersed catalytic components such as platinum group metals. For this reason the honeycomb carrier is conventionally coated with a thin coating of a high surface area micropore-containing refractory metal oxide on which the catalytic metal component is dispersed. Any suitable high surface area refractory metal oxide is employable as the metal oxide support coating. For example, alumina, preferably active or calcined alumina, beryllia, zirconia, magnesia, silica and combinations of metal oxides such as boria-alumina and silica-alumina, may be employed. High surface area aluminas (which include the chi, gamma, eta, kappa, theta and delta forms) are the most commonly used support coatings. The alumina is usually stabilized against high temperature phase change to low surface area alpha alumina by inclusion therein of additives such as one or more rare earth metal oxides.
Compositions as described in the aforesaid U.S. patents have found particular utility as internal combustion engine exhaust gas pollution abatement catalysts. Similar catalyst compositions have been found useful for other applications including, as disclosed in U.S. Pat. No. 3,928,961, catalytically oxidizing a fuel in a combination operation for purposes of energy production.
In all such applications a gaseous stream (which may comprise a fuel or combustible pollutants and oxygen in cases where oxidation is to be carried out) is passed over the catalyst, and reactive components of the gas stream must contact the catalytic metal component in order to catalyze the reaction. It is therefore necessary that the refractory support coating on which the catalytic metal component is dispersed, and in which a substantial portion of it may be embedded, be sufficiently porous to admit the passage of the gaseous reactants therethrough to contact the catalytic metal component dispersed thereon.